The purpose of this project is to identify, primarily by two-dimensional gel electrophoresis, polypeptides that characterize the cell surface in normal and neoplastic cells. Studies on normal hepatocytes from rats at different stages of development and from regenerating livers will be compared to studies on preneoplastic and neoplastic liver cell populations in order to identify alterations in cell surface polypeptide patterns that distinguish the malignant cell from the normal cell. Major findings are as follows: (1) The optimum method for the surface iodination of cells maintained as monolayers in 55 mm diameter tissue culture dishes utilized 1 mCi of Na[125-I] per dish and the direct addition of hydrogen peroxide to cells bathed in a lactoperoxidase-PBS-Na[125-I] solution at 2-4 C. (2) Transferrin-Sepharose beads were used to extract the transferrin receptor from a Triton X-100 extract of cells that had been surface-labeled with radioactive iodine. Two-dimensional gel electrophoresis of the isolated transferrin receptor and of the complete mixture of labeled cell surface proteins allowed identification of the position of this receptor on the autoradiogram of the complete mixture. (3) Preliminary manual analysis of autoradiograms of the two-dimensional gel electrophoresis patterns of radioiodinated cell surface proteins from normal and preneoplastic cells indicated that, with respect to control hepatocytes, preneoplastic hepatocyte cell surface patterns gain four spot/spot groups and lose one spot.